A nonlinear galloping energy harvester with quasi-zero stiffness

One of the design requirements to enhance the performance of a galloping piezoelectric energy harvester (GPEH) is to have a low natural frequency. A nonlinear system with a zero local linearised stiffness about the working point, known as a Quasi-Zero-Stiffness (QZS) can be employed to achieve ultra-low natural frequency. The energy is harvested by attaching a piezoelectric sheet to the transverse degree of freedom of the harvester. In this paper, an aero-electro-mechanical model of the QZS nonlinear GPEH is obtained, with the QZS mechanism formed by adding two transverse springs to the GPEH. Numerical integration demonstrates that a QZS nonlinear GPEH with a lower and flatter stiffness-displacement curve can harvest more power than one with a higher and steeper curve. An analytical solution using the harmonic balance method (HBM) was obtained and used to optimise the system. It is shown that three optimal values of the mechanical to electrical time-constant ratio exist for the QZS nonlinear GPEH. Also, a relative performance study was performed, and it is shown that the QZS GPEH has the potential to harvest more power than the conventional GPEH.